Communication circuit with single element antenna for multi-frequency applications

ABSTRACT

A communication circuit according to one embodiment includes a single element antenna, a plurality of signal-limiting circuits, a high-frequency transceiver circuit, and a low-frequency transceiver circuit. The high-frequency transceiver circuit is adapted to be selectively coupled to the single element antenna via the plurality of signal-limiting circuits and tuned to operate at a high frequency carrier frequency, and the low-frequency transceiver circuit is adapted to be selectively coupled to the single element antenna via the plurality of signal-limiting circuits and tuned to operate at a low frequency carrier frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 15/823,802 filed on Nov. 28, 2017, the contents ofwhich are incorporated herein by reference in their entirety.

BACKGROUND

A reader is a device that can be used to communicate with credentialdevices (e.g., cards, fobs, tags, phones, etc.) in access controlsystems, credential systems, and other systems. The reader may read datafrom the credential and the reader may write data to the credential.

Generally, the credential device is an active or passive radio frequency(RF) communication device that can wirelessly communicate with variousdevices in the system (e.g., readers, access control devices, etc.).Passive credential devices rely on another device to supply power to thepassive credential device by virtue of an excitation signal, whereasactive credential devices supply their own power. Common passivecredential devices include proximity cards, which communicate via datasignals transmitted at a nominal carrier frequency of 125 kHz, andsmartcards, which communicate via data signals transmitted at a nominalcarrier frequency of 13.56 MHz.

SUMMARY

One embodiment is a unique system, components, and methods for a singleelement antenna. Other embodiments include apparatuses, systems,devices, hardware, methods, and combinations for a single elementantenna. This summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used asan aid in limiting the scope of the claimed subject matter. Furtherembodiments, forms, objects, features, advantages, aspects, and benefitsshall become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The concepts described herein are illustrative by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. Where considered appropriate, referenceslabels have been repeated among the figures to indicate corresponding oranalogous elements.

FIG. 1 is a simplified block diagram of at least one embodiment of asystem for multi-frequency communication;

FIG. 2 is a simplified block diagram of at least one embodiment of acomputing system;

FIGS. 3-5 are simplified diagrams of at least one embodiment of thecommunication circuit of FIG. 1;

FIGS. 6-8 illustrate various embodiments of the single element antennaof FIG. 5;

FIG. 9 is a simplified diagram of at least one embodiment of thehigh-frequency (HF) transceiver circuit of FIGS. 3-5;

FIG. 10 is a simplified block diagram of at least one embodiment of thelow-frequency (LF) transceiver circuit of FIGS. 3-5;

FIGS. 11 and 12 are simplified diagrams of other embodiments of thecommunication circuit of FIG. 1; and

FIG. 13 is a simplified diagram of at least one other embodiment of thecommunication circuit of FIG. 1.

DETAILED DESCRIPTION

Although the concepts of the present disclosure are susceptible tovarious modifications and alternative forms, specific embodiments havebeen shown by way of example in the drawings and will be describedherein in detail. It should be understood, however, that there is nointent to limit the concepts of the present disclosure to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives consistent with the presentdisclosure and the appended claims.

References in the specification to “one embodiment,” “an embodiment,”“an illustrative embodiment,” etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may or may not necessarily includethat particular feature, structure, or characteristic. Moreover, suchphrases are not necessarily referring to the same embodiment. It shouldfurther be appreciated that although reference to a “preferred”component or feature may indicate the desirability of a particularcomponent or feature with respect to an embodiment, the disclosure isnot so limiting with respect to other embodiments, which may omit such acomponent or feature. Further, when a particular feature, structure, orcharacteristic is described in connection with an embodiment, it issubmitted that it is within the knowledge of one skilled in the art toimplement such feature, structure, or characteristic in connection withother embodiments whether or not explicitly described. Additionally, itshould be appreciated that items included in a list in the form of “atleast one of A, B, and C” can mean (A); (B); (C); (A and B); (B and C);(A and C); or (A, B, and C). Similarly, items listed in the form of “atleast one of A, B, or C” can mean (A); (B); (C); (A and B); (B and C);(A and C); or (A, B, and C). Further, with respect to the claims, theuse of words and phrases such as “a,” “an,” “at least one,” and/or “atleast one portion” should not be interpreted so as to be limiting toonly one such element unless specifically stated to the contrary, andthe use of phrases such as “at least a portion” and/or “a portion”should be interpreted as encompassing both embodiments including only aportion of such element and embodiments including the entirety of suchelement unless specifically stated to the contrary.

The disclosed embodiments may, in some cases, be implemented inhardware, firmware, software, or a combination thereof. The disclosedembodiments may also be implemented as instructions carried by or storedon one or more transitory or non-transitory machine-readable (e.g.,computer-readable) storage media, which may be read and executed by oneor more processors. A machine-readable storage medium may be embodied asany storage device, mechanism, or other physical structure for storingor transmitting information in a form readable by a machine (e.g., avolatile or non-volatile memory, a media disc, or other media device).

In the drawings, some structural or method features may be shown inspecific arrangements and/or orderings. However, it should beappreciated that such specific arrangements and/or orderings may not berequired. Rather, in some embodiments, such features may be arranged ina different manner and/or order than shown in the illustrative figuresunless indicated to the contrary. Additionally, the inclusion of astructural or method feature in a particular figure is not meant toimply that such feature is required in all embodiments and, in someembodiments, may not be included or may be combined with other features.

Referring now to FIG. 1, in the illustrative embodiment, a system 100for multi-frequency communication includes a radio frequency (RF) reader102 and one or more passive RF devices 104. Additionally, in someembodiments, the system 100 may include one or more active RF devices106. In particular, the illustrative passive RF devices 104 include aproximity card 108 and a smartcard 110; however, it should beappreciated that the system 100 may include additional and/oralternative passive RF devices 104 in other embodiments. As described indetail below, the RF reader 102 includes a communication circuit 112having a single element antenna 302 that enables communication withRF-capable devices over multiple different carrier frequencies. Forexample, in the illustrative embodiment, the RF reader 102 is capable ofwirelessly communicating with the proximity card 108 using the singleelement antenna 302 via RF signals at a nominal carrier frequency of 125kHz (e.g., within the range of approximately 100-150 kHz) and wirelesslycommunicating with the smartcard 110 using the single element antenna302 via RF signals at a nominal carrier frequency of 13.56 MHz.

A single element antenna is one continuous conductor withoutinterference (or minimal interference) from other components such as,but not limited to, passive components, integrated circuits (ICs), orswitches. The one continuous conductor may include a stub or resonantstub. Furthermore, the one continuous conductor may include one or moreconducting mediums such as a copper wire and/or a printed circuit board(PCB) trace, and may include different gauges of wire or trace widths.

It should be appreciated that the RF reader 102 may be embodied as anydevice suitable for including the communication circuit 112 for wirelessRF communication with other devices (e.g., passive RF devices 104 and/oractive RF devices 106) based on the techniques and mechanisms describedherein. For example, in some embodiments, the RF reader 102 may beembodied as an enrollment reader, reader/writer device, access controldevice, kiosk, and/or other suitable device. In embodiments in which theRF reader 102 is embodied as an access control device, the accesscontrol device may be configured to control access through one or morecorresponding passageways (e.g., via a lock mechanism such as adeadbolt, latch bolt, lever, and/or other mechanism adapted to movebetween a locked and unlocked state). However, it should be appreciatedthat the access control device may be embodied as another type of accesscontrol device in other embodiments. In some embodiments, the RF reader102 may be embodied as one or more computing devices similar to thecomputing device 200 described below in reference to FIG. 2. Forexample, in the illustrative embodiment, the RF reader 102 includes aprocessing device 202 and a memory 206 having stored thereon operatinglogic 208 for execution by the processing device 202 for operation ofthe RF reader 102. Further, in embodiments including an active RFdevice, the active RF device may be embodied as a computing devicesimilar to the computing device 200 of FIG. 2.

Referring now to FIG. 2, a simplified block diagram of at least oneembodiment of a computing device 200 is shown. The illustrativecomputing device 200 depicts at least one embodiment of a RF reader thatmay be utilized in connection with the RF reader 102 illustrated inFIG. 1. Depending on the particular embodiment, the computing device 200may be embodied as a reader device, enrollment device, credentialdevice, access control device, server, desktop computer, laptopcomputer, tablet computer, notebook, netbook, Ultrabook™, mobilecomputing device, cellular phone, smartphone, wearable computing device,personal digital assistant, Internet of Things (IoT) device, controlpanel, processing system, router, gateway, and/or any other computing,processing, and/or communication device capable of performing thefunctions described herein.

The computing device 200 includes a processing device 202 that executesalgorithms and/or processes data in accordance with operating logic 208,an input/output device 204 that enables communication between thecomputing device 200 and one or more external devices 210, and memory206 which stores, for example, data received from the external device210 via the input/output device 204.

The input/output device 204 allows the computing device 200 tocommunicate with the external device 210. For example, the input/outputdevice 204 may include a transceiver, a network adapter, a network card,an interface, one or more communication ports (e.g., a USB port, serialport, parallel port, an analog port, a digital port, VGA, DVI, HDMI,FireWire, CAT 5, or any other type of communication port or interface),and/or other communication circuitry. Communication circuitry of thecomputing device 200 may be configured to use any one or morecommunication technologies (e.g., wireless or wired communications) andassociated protocols (e.g., Ethernet, Bluetooth®, Wi-Fi®, WiMAX, etc.)to effect such communication depending on the particular computingdevice 200. The input/output device 204 may include hardware, software,and/or firmware suitable for performing the techniques described herein.

The external device 210 may be any type of device that allows data to beinputted or outputted from the computing device 200. For example, invarious embodiments, the external device 210 may be embodied as the RFreader 102, one or more of the passive RF devices 104, and/or one ormore of the active RF devices 106. Further, in some embodiments, theexternal device 210 may be embodied as another computing device, switch,diagnostic tool, controller, printer, display, alarm, peripheral device(e.g., keyboard, mouse, touch screen display, etc.), and/or any othercomputing, processing, and/or communication device capable of performingthe functions described herein. Furthermore, in some embodiments, itshould be appreciated that the external device 210 may be integratedinto the computing device 200.

The processing device 202 may be embodied as any type of processor(s)capable of performing the functions described herein. In particular, theprocessing device 202 may be embodied as one or more single ormulti-core processors, microcontrollers, or other processor orprocessing/controlling circuits. For example, in some embodiments, theprocessing device 202 may include or be embodied as an arithmetic logicunit (ALU), central processing unit (CPU), digital signal processor(DSP), and/or another suitable processor(s). The processing device 202may be a programmable type, a dedicated hardwired state machine, or acombination thereof. Processing devices 202 with multiple processingunits may utilize distributed, pipelined, and/or parallel processing invarious embodiments. Further, the processing device 202 may be dedicatedto performance of just the operations described herein, or may beutilized in one or more additional applications. In the illustrativeembodiment, the processing device 202 is of a programmable variety thatexecutes algorithms and/or processes data in accordance with operatinglogic 208 as defined by programming instructions (such as software orfirmware) stored in memory 206. Additionally or alternatively, theoperating logic 208 for processing device 202 may be at least partiallydefined by hardwired logic or other hardware. Further, the processingdevice 202 may include one or more components of any type suitable toprocess the signals received from input/output device 204 or from othercomponents or devices and to provide desired output signals. Suchcomponents may include digital circuitry, analog circuitry, or acombination thereof.

The memory 206 may be of one or more types of non-transitorycomputer-readable media, such as a solid-state memory, electromagneticmemory, optical memory, or a combination thereof. Furthermore, thememory 206 may be volatile and/or nonvolatile and, in some embodiments,some or all of the memory 206 may be of a portable variety, such as adisk, tape, memory stick, cartridge, and/or other suitable portablememory. In operation, the memory 206 may store various data and softwareused during operation of the computing device 200 such as operatingsystems, applications, programs, libraries, and drivers. It should beappreciated that the memory 206 may store data that is manipulated bythe operating logic 208 of processing device 202, such as, for example,data representative of signals received from and/or sent to theinput/output device 204 in addition to or in lieu of storing programminginstructions defining operating logic 208. As shown in FIG. 2, thememory 206 may be included with the processing device 202 and/or coupledto the processing device 202 depending on the particular embodiment. Forexample, in some embodiments, the processing device 202, the memory 206,and/or other components of the computing device 200 may form a portionof a system-on-a-chip (SoC) and be incorporated on a single integratedcircuit chip.

In some embodiments, various components of the computing device 200(e.g., the processing device 202 and the memory 206) may becommunicatively coupled via an input/output subsystem, which may beembodied as circuitry and/or components to facilitate input/outputoperations with the processing device 202, the memory 206, and othercomponents of the computing device 200. For example, the input/outputsubsystem may be embodied as, or otherwise include, memory controllerhubs, input/output control hubs, firmware devices, communication links(i.e., point-to-point links, bus links, wires, cables, light guides,printed circuit board traces, etc.) and/or other components andsubsystems to facilitate the input/output operations.

The computing device 200 may include other or additional components,such as those commonly found in a typical computing device (e.g.,various input/output devices and/or other components), in otherembodiments. It should be further appreciated that one or more of thecomponents of the computing device 200 described herein may bedistributed across multiple computing devices. In other words, thetechniques described herein may be employed by a computing system thatincludes one or more computing devices. Additionally, although only asingle processing device 202, I/O device 204, and memory 206 areillustratively shown in FIG. 2, it should be appreciated that aparticular computing device 200 may include multiple processing devices202, I/O devices 204, and/or memories 206 in other embodiments. Further,in some embodiments, more than one external device 210 may be incommunication with the computing device 200.

Referring back to FIG. 1, it should further be appreciated that theillustrative RF reader 102 includes the communication circuit 112. Asindicated above, the communication circuit 112 of the RF reader 102includes the single element antenna 302 and enables communication withRF-capable devices over multiple different carrier frequencies. In someembodiments, the communication circuit 112 may be embodied as (orinclude the entirety or a portion of) the communication circuit 300 ofFIGS. 3-5, the communication circuit 1000 of FIG. 10, or thecommunication circuit 1100 of FIG. 11.

The active RF device(s) 106 may be embodied as any non-passive devicecapable of communicating with the RF reader 102 via RF signals (e.g., aself-powered RF communication device) and otherwise performing thefunctions described herein. For example, each of the active RF device(s)106 may be embodied as a computing device similar to the computingdevice 200 described above in reference to FIG. 2. In particular, insome embodiments, one or more of the active RF device(s) 106 may beembodied as a mobile computing device such as a laptop computer, tabletcomputer, notebook, netbook, Ultrabook™, cellular phone, smartphone,wearable computing device, personal digital assistant, Internet ofThings (IoT) device and/or another mobile computing device capable ofperforming the functions described herein.

As indicated above, the proximity card 108 is a passive RF devicecapable of wirelessly communicating with the RF reader 102 at a nominalcarrier frequency of 125 kHz. As such, in the illustrative embodiment,the proximity card 108 is not physically coupled to a power supply;instead, the proximity card 108 is powered by virtue of electromagneticwaves (i.e., excitation signals) transmitted by the RF reader 102 whenthe RF reader 102 is within a certain range of the proximity card 108.As shown in FIG. 1, the illustrative proximity card 108 includes anintegrated circuit 114 electrically coupled to one or more antennas 116.Although the proximity card 108 may include additional and/oralternative components, those components are omitted herein for clarityof the description. When the RF reader 102 is within a sufficientdistance of the proximity card 108, the integrated circuit 114 ispowered by virtue of excitation signals received by the proximity card108. The integrated circuit 114 includes a memory including variousinstructions and data (e.g., one or more unique identifiers associatedwith the proximity card 108 or user thereof) and a processor that, whenpowered, is capable of processing the instructions stored on the memory,for example, to read data from the memory, write data to the memory,and/or communicate with the RF reader 102 via the antenna(s) 116.

The smartcard 110 is a passive RF device capable of wirelesslycommunicating with the RF reader 102 at a nominal frequency of 13.56MHz. Similar to the proximity card 108, the smartcard 110 is notphysically coupled to a power supply and, therefore, must be powered byvirtue of electromagnetic waves transmitted by the RF reader 102 whenthe RF reader 102 is within a sufficient distance to provide suchexcitation signals. Additionally, the illustrative smartcard 110includes an integrated circuit 118 that is electrically coupled to oneor more antennas 120. In some embodiments, the integrated circuit 118and the antenna(s) 120 of the smartcard 110 may be similar to theintegrated circuit 114 and the antenna(s) 116 of the proximity card 108.As such, the description of the integrated circuit 114 and theantenna(s) 116 is equally applicable to the corresponding components ofthe smartcard 110 and has not been repeated herein for clarity of thedescription. In some embodiments, it should be appreciated that thesmartcard 110 may include additional functionality relative to theproximity card 108. For example, in some embodiments, after the initialprovisioning of the proximity card 108, the proximity card 108 mayprovide read-only access to the data stored thereon, whereas thesmartcard 110 may provide read-write access to the data stored thereon.Additionally, although the proximity card 108 and the smartcard 110 aredescribed herein as “cards,” it should be appreciated that the proximitycard 108 and/or the smartcard 110 may be in any physical form suitablefor performing the functions described herein. For example, in variousembodiments, the proximity card 108 and/or the smartcard 110 may beembodied as a tag, fob, pin, or other suitable device. In someembodiments, the card 108, 110 may be integrated into another physicaldevice/mechanism.

Although only one RF reader 102, one active RF device 106, one proximitycard 108, and one smartcard 110 are shown in the illustrative embodimentof FIG. 1, the system 100 may include multiple RF readers 102, active RFdevices 106, proximity cards 108, and/or smartcards 110 in otherembodiments. For example, a particular RF reader 102 may be configuredto communicate with myriad other RF devices 104, 106. Further, it shouldbe appreciated that, in various embodiments, the system 100 may includeany number and type of passive RF devices 104.

In some embodiments, it should be appreciated that the communicationcircuit 112 of the RF reader 102 may be embodied as the communicationcircuit 300 illustrated in FIGS. 3-5. Referring now to FIGS. 3-5, theillustrative communication circuit 300 includes a single element antenna302, a processor 304, a high-frequency (HF) transceiver circuit 306, anda low-frequency (LF) transceiver circuit 308. As described herein, thehigh-frequency transceiver circuit 306 enables wireless communicationwith RF devices 104, 106 over a high frequency carrier frequency. Inparticular, in the illustrative embodiment, the high-frequencytransceiver circuit 306 enables wireless RF communication with thesmartcard 110 over a high frequency carrier frequency that is nominally13.56 MHz. Further, the low-frequency transceiver circuit 308 enableswireless communication with RF devices 104, 106 over a low frequencycarrier frequency. In particular, in the illustrative embodiment, thelow-frequency transceiver circuit 308 enables wireless RF communicationwith the proximity card 108 over a low frequency carrier frequency thatis nominally 125 kHz.

The illustrative communication circuit 300 further includessignal-limiting circuits 310, 312, 314. Although the signal-limitingcircuits 310, 312, 314 of the communication circuit 300 are depicted asswitches, it should be appreciated that one or more of thesignal-limiting circuits 310, 312, 314 may be embodied as another typeof signal-limiting circuit. For example, in various embodiments, thesignal-limiting circuits 310, 312, 314 may be embodied as electricalswitches, electromechanical switches, solid state switches,electromechanical relays, solid state relays, transistors, activefilters, passive filters (e.g., circuits including resistors,capacitors, and/or inductors), and/or other signal-limiting circuitscapable of performing the functions described herein.

In the illustrative embodiment, it should be appreciated that the singleelement antenna 302 is embodied as a single continuous conductor havingtwo portions 316, 318. The first portion 316 is defined between a firstnode 320 and a second node 322, and the second portion 318 is definedbetween the second node 322 and a third node 324. As shown, theillustrative high-frequency transceiver circuit 306 has electricalterminals 326, 328, and the low-frequency transceiver circuit 308 haselectrical terminals 330, 332. Further, in the illustrative embodiment,the signal-limiting circuit 310 is coupled to the first node 320 and theterminals 326, 330; the signal-limiting circuit 312 is coupled to thesecond node 322 and the terminal 328; and the signal-limiting circuit314 is coupled to the third node 324 and the terminal 332. Morespecifically, in some embodiments, the signal-limiting circuit 310 maybe “switched” between a state in which the first node 320 iselectrically coupled to the terminal 326 and a state in which the firstnode 320 is electrically coupled to the terminal 330. Further, in someembodiments, the signal-limiting circuit 312 may be “switched” between astate in which the second node 322 is decoupled from the terminal 328(e.g., an open state) and a state in which the second node 322 iselectrically coupled to the terminal 328 (e.g., a closed state).Additionally, in some embodiments, the signal-limiting circuit 314 maybe “switched” between a state in which the third node 324 is decoupledfrom the terminal 332 (e.g., an open state) and a state in which thethird node 324 is electrically coupled to the terminal 332 (e.g., aclosed state).

As shown, the illustrative communication circuit 300 further includesthe processor 304, which is communicatively coupled to thehigh-frequency transceiver circuit 306, the low-frequency transceivercircuit 308, and the signal-limiting circuits 310, 312, 314 for controlthereof. In particular, the processor 304 is communicatively coupled tothe high-frequency transceiver circuit 306 via an electrical connection334 and is communicatively coupled to the low-frequency transceivercircuit 308 via an electrical connection 336. Additionally, theprocessor 304 is communicatively coupled to the signal-limiting circuits310, 312, 314 via electrical connections 338, 340, 342, respectively. Itshould be appreciated that the electrical connections 334, 336, 338,340, 342 may be embodied as any type of electrical connections thatallow the processor 304 to communicate with the corresponding circuitsand otherwise perform the functions described herein. For example, insome embodiments, the electrical connections 334, 336 may be embodied asdigital control connections that allow the processor 304 to interactwith the high-frequency transceiver circuit 306 and the low-frequencytransceiver circuit 308 via a SPI interface. Further, in someembodiments, the electrical connections 338, 340, 342 may be embodied asgeneral purpose input/output (GPIO) connections that allow the processor304 to interact with the signal-limiting circuits 310, 312, 314 (e.g.,electrical switches).

It should be appreciated that the processor 304 may be embodied as anyprocessor or processing device suitable for performing the functionsdescribed herein. For example, in some embodiments, the processor 304may be embodied as a processing device similar to the processing device202 described above in reference to FIG. 2. In particular, the processor304 may be embodied as, or otherwise include, a microprocessor,microcontroller, arithmetic logic unit, central processing unit, digitalsignal processor, and/or other suitable processor. The processor 304 andthe connections 334, 336, 338, 340, 342 have been omitted from FIGS. 4-5for clarity of the description.

As shown in reference to FIGS. 3-5, the illustrative processor 304 isconfigured to control the signal-limiting circuits 310, 312, 314 toselectively couple the high-frequency transceiver circuit 306 and thelow-frequency transceiver circuit 308 to the single element antenna 302for communication with remote devices via the corresponding carrierfrequency. As shown in FIG. 4, in a first mode of operation, theprocessor 304 controls the signal-limiting circuits 310, 312, 314 toelectrically couple/connect the high-frequency transceiver circuit 306to the single element antenna 302 and decouple/disconnect thelow-frequency transceiver circuit 308 from the single element antenna302. Accordingly, in the first mode of operation, the processor 304 isconfigured to power and received data from RF devices 104, 106 (e.g.,the smartcard 110) over the high frequency carrier frequency (e.g.,13.56 MHz). In the first mode of operation in which the high-frequencytransceiver circuit 306 is electrically coupled to the single elementantenna 302 for communication over the high frequency carrier frequency,it should be appreciated that the portion 318 of the single elementantenna 302 exhibits one or more electromagnetic characteristics of aresonant stub (i.e., the portion 318 acts as a passive RFcomponent/element), which are filtered by the high-frequency transceivercircuit 306. As shown in FIG. 5, in a second mode of operation, theprocessor 304 controls the signal-limiting circuits 310, 312, 314 toelectrically couple/connect the low-frequency transceiver circuit 308 tothe single element antenna 302 and decouple/disconnect thehigh-frequency transceiver circuit 306 from the single element antenna302. Accordingly, in the second mode of operation, the processor 304 isconfigured to power and received data from RF devices 104, 106 (e.g.,the proximity card 108) over the low frequency carrier frequency (e.g.,125 kHz).

More specifically, in the first mode of operation in which communicationvia the high-frequency transceiver circuit 306 is enabled, thesignal-limiting circuit 310 is in the state in which the first node 320is electrically coupled to the terminal 326, the signal-limiting circuit312 is in the state in which the second node 322 is electrically coupledto the terminal 328, and the signal-limiting circuit 314 is in the statein which the third node 324 is decoupled from the terminal 332. In thesecond mode of operation in which communication via the low-frequencytransceiver circuit 308 is enabled, the signal-limiting circuit 310 isin the state in which the first node 320 is electrically coupled to theterminal 330, the signal-limiting circuit 314 is in the state in whichthe third node 324 is electrically coupled to the terminal 332, and thesignal-limiting circuit 312 is in the state in which the second node 322is decoupled from the terminal 328.

It should be appreciated that the single element antenna 302 may beembodied as any type of antenna having a single shared conductiveelement suitable for performing the functions described herein andotherwise consistent with the description. For example, in theillustrative embodiment, the single element antenna 302 is embodied as acoil antenna and, in some embodiments, the single element antenna 302may be structured such that its coils are physically positioned,partially or entirely, on the same shared plane as one another (e.g.,printed on or integrated within a PCB substrate, a flex PCB, and/oranother suitable substrate). In such embodiments, it should beappreciated that the portion 316 of the single element antenna 302 isembodied as first portion of coils and the portion 318 is embodied as asecond portion of coils. As such, in the first mode of operation, thefirst portion of coils is used for transmitting and receiving wirelesscommunication using the high-frequency transceiver circuit 306 and thesecond portion of coils has one or more electromagnetic characteristicsof a resonant stub, which may be accounted for by the high-frequencytransceiver circuit 306. In the second mode of operation, both the firstportion and the second portion of coils are used for transmitting andreceiving wireless communication using the low-frequency transceivercircuit 308.

In various embodiments, the single element antenna 302 may be embodiedas the single element coil antenna 600 of FIG. 6, the single elementcoil antenna 700 of FIG. 7, or the single element coil antenna 800 ofFIG. 8. As illustrated by the illustrative antennas 600, 700, 800, itshould be appreciated that each of the first portion 316 and the secondportion 318 of the single element antenna 302 may include any number ofconductive coils, and the diameter(s) and spacing of the coils may varydepending on the particular embodiment. For example, in someembodiments, the first coil portion 316 may be a conductive coil portionof a first diameter having a first number of windings, and the secondcoil portion 318 may be a conductive coil portion of a second diameterhaving a second number of windings. The first diameter may be the sameor different from the second diameter and/or the first number may be thesame or different from the second number depending on the particularembodiment. In some embodiments, in order to achieve the neededinductance for low frequency communication, the second portion of coilsincludes many windings (e.g., greater than one hundred windings).Further, it should be appreciated that in order to integrate the coilcharacteristics into a PCB, for example, the trace size, space size,layer stack, and/or antenna pattern may vary depending on the particularembodiment.

Referring back to FIG. 3, it should be appreciated that thehigh-frequency transceiver circuit 306 and the low-frequency transceivercircuit 308 may be embodied as any circuits suitable for performing thefunctions described herein. For example, in some embodiments, thehigh-frequency transceiver circuit 306 and/or the low-frequencytransceiver circuit 308 may be embodied as or otherwise include anintegrated circuit. For example, in the illustrative embodiment, thehigh-frequency transceiver circuit 306 may be embodied as or otherwiseinclude a CLRC663 integrated circuit manufactured by NXP SemiconductorsN.V. of Eindhoven, Netherlands. In particular, in some embodiments, thehigh-frequency transceiver circuit 306 may be embodied as ahigh-frequency transceiver circuit similar to the high-frequencytransceiver circuit 900 of FIG. 9.

Referring now to FIG. 9, the illustrative high-frequency transceivercircuit 900 includes a CLRC663 integrated circuit 902, anelectromagnetic compatibility (EMC) filter 904, and a matching circuit906. The CLRC663 integrated circuit 902 may perform the variousprocessing functions described above in reference to the high-frequencytransceiver circuit 306 (e.g., facilitating communication with asmartcard 110 over the high-frequency carrier frequency). Although theintegrated circuit 902 is described herein as being embodied as theCLRC663 integrated circuit 902, it should be appreciated that theintegrated circuit 902 may be embodied as another suitable integratedcircuit or processor in other embodiments. The EMC filter 904 may reduceor eliminate the transfer of electromagnetic noise throughout and/orto/from the circuit 900. The matching circuit 906 may serve as animpedance matching circuit that functions to ensure the source and loadimpedances match to thereby maximize power transfer. Although theillustrative matching circuit 906 leverages capacitors to perform thematching, it should be appreciated that the matching circuit 906 mayadditionally or alternatively include inductors and/or other circuitelements in other embodiments. Further, it should be appreciated thatthe high-frequency transceiver circuit 900 may include additional oralternative components in various embodiments.

In some embodiments, the low-frequency transceiver circuit 308 may beembodied as a low-frequency transceiver circuit similar to thelow-frequency transceiver circuit 1000 of FIG. 10. Referring now to FIG.10, the illustrative low-frequency transceiver circuit 1000 includes aprocessor pulse width modulator (PWM) 1002, a coil driver 1004, one ormore active bandpass filters 1006, and one or more processor inputcapture timers 1008. The processor PWM 1002 generates a pulse widthmodulated signal that is converted into a low frequency analog signal(e.g., 125 kHz) by the coil driver 1004 for transmission to thecorresponding RF device 104, 106 via the single element antenna 302.Upon receiving a signal via the single element antenna 302 in the lowfrequency mode, the active bandpass filter(s) 1006 filters the receivedsignal, which is passed to the processor input capture timer(s) 1008 forfurther processing. In order to perform the corresponding functions, itshould be appreciated that the low-frequency transceiver circuit 1000and/or components thereof may include one or more components notillustrated in FIG. 10 for simplicity. For example, in some embodiments,the coil driver 1004 may include one or more transistors (e.g.,MOSFETs), inductors, and/or tuning devices (e.g., capacitors) and/or theactive bandpass filter(s) 1006 may include one or more discretecomponents and/or operational amplifiers.

Referring now to FIG. 11, it should be appreciated that, in someembodiments, one or more of the signal-limiting circuits 310, 312, 314may be embodied as, or replaced by, filter circuits. In particular, inthe illustrative embodiment, the signal-limiting circuit 310 may includefilter circuits 1102, 1104, the signal-limiting circuit 312 may includea filter circuit 1106, and the signal-limiting circuit 314 may include afilter circuit 1108. More specifically, the filter circuit 1102 may beelectrically coupled to the first node 320 and the terminal 330 of thelow-frequency transceiver circuit 308, the filter circuit 1104 may beelectrically coupled to the first node 320 and the terminal 326 of thehigh-frequency transceiver circuit 306, the filter circuit 1106 may beelectrically coupled to the second node 322 and the high-frequencytransceiver circuit 306, and the filter circuit 1108 may be electricallycoupled to the third node 324 and the low-frequency transceiver circuit308. Depending on the particular embodiment, each of the filter circuits1102, 1104, 1106, 1108 may be embodied as one or more lowpass filters,highpass filters, and/or bandpass filters configured to block/limitsignals consistent with the techniques described herein. Further, eachof the filter circuits 1102, 1104, 1106, 1108 may be embodied as anactive or passive filter. As such, in embodiments in which each of thefilter circuits 1102, 1104, 1106, 1108 is embodied as a passive filter,it should be appreciated that the control circuit 1100 may eliminate theneed for logic control (e.g., by the processor 304). For example, insome embodiments, a passive filter may be embodied as a filter with acutoff frequency such that signals are preventing from entering thehigh-frequency transceiver circuit 306 from the low-frequencytransceiver circuit 308 and/or preventing from entering thelow-frequency transceiver circuit 308 from the high-frequencytransceiver circuit 306.

Referring now to FIG. 12, in some embodiments, the signal-limitingcircuits 310, 312, 314 may be omitted from the communication circuit1200. For example, in some embodiments, the high-frequency transceivercircuit 306 and the low-frequency transceiver circuit 308 may includehigh impedance modes such that additional “switching” and/or filteringare unnecessary. Accordingly, in the illustrative embodiment of FIG. 12,the high-frequency transceiver circuit 306 is electrically coupleddirectly to the first node 320 and the second node 322, and thelow-frequency transceiver circuit 308 is electrically coupled directlyto the first node 320 and the third node 324.

In some embodiments, the communication circuit 112 of the RF reader 102may be embodied as the communication circuit 1300 illustrated in FIG.13. Referring now to FIG. 13, the illustrative communication circuit1300 includes a single element antenna 302, a processor 304, ahigh-frequency (HF) transceiver circuit 306, and a low-frequency (LF)transceiver circuit 308. It should be appreciated that those circuitsand components are similar to the corresponding circuits and componentsof the communication circuit 300 of FIG. 3 and, therefore, thedescription of those components is not repeated herein for brevity ofthe description.

The illustrative communication circuit 1300 further includessignal-limiting circuits 1310, 1312, 1314, 1316. Although thesignal-limiting circuits 1310, 1312, 1314, 1316 of the communicationcircuit 1300 are depicted as switches, it should be appreciated that oneor more of the signal-limiting circuits 1310, 1312, 1314, 1316 may beembodied as another type of signal-limiting circuit. For example, invarious embodiments, the signal-limiting circuits 1310, 1312, 1314, 1316may be embodied as electrical switches, electromechanical switches,solid state switches, electromechanical relays, solid state relays,transistors, active filters, passive filters (e.g., circuits includingresistors, capacitors, and/or inductors), and/or other signal-limitingcircuits capable of performing the functions described herein.

In the illustrative embodiment, it should be appreciated that the singleelement antenna 302 is embodied as a single continuous conductor havingthree portions 1318, 1320, 1322. The first portion 1318 is definedbetween a first node 1324 and a second node 1326, the second portion1320 is defined between the second node 1326 and a third node 1328, andthe third portion 1322 is defined between the third node 1328 and afourth node 1330. As shown, the illustrative high-frequency transceivercircuit 306 has electrical terminals 1332, 1334, and the low-frequencytransceiver circuit 308 has electrical terminals 1336, 1338. Further, inthe illustrative embodiment, the signal-limiting circuit 1310 is coupledto the first node 1324 and the terminal 1336, the signal-limitingcircuit 1312 is coupled to the second node 1326 and the terminal 1332,the signal-limiting circuit 1314 is coupled to the third node 1328 andthe terminal 1334, and the signal-limiting circuit 1316 is coupled tothe fourth node 1330 and the terminal 1338. More specifically, in someembodiments, the signal-limiting circuit 1310 may be “switched” betweena state in which the first node 1324 is decoupled from the terminal 1336(e.g., an open state) and a state in which the first node 1324 iselectrically coupled to the terminal 1336 (e.g., a closed state).Further, in some embodiments, the signal-limiting circuit 1312 may be“switched” between a state in which the second node 1326 is decoupledfrom the terminal 1332 (e.g., an open state) and a state in which thesecond node 1326 is electrically coupled to the terminal 1332 (e.g., aclosed state). Additionally, in some embodiments, the signal-limitingcircuit 1314 may be “switched” between a state in which the third node1328 is decoupled from the terminal 1334 (e.g., an open state) and astate in which the third node 1328 is electrically coupled to theterminal 1334 (e.g., a closed state). In some embodiments, thesignal-limiting circuit 1316 may be “switched” between a state in whichthe fourth node 1330 is decoupled from the terminal 1338 (e.g., an openstate) and a state in which the fourth node 1330 is electrically coupledto the terminal 1338 (e.g., a closed state).

As shown, the illustrative communication circuit 1300 further includesthe processor 304, which is communicatively coupled to thehigh-frequency transceiver circuit 306, the low-frequency transceivercircuit 308, and the signal-limiting circuits 1310, 1312, 1314, 1316 forcontrol thereof. In particular, the processor 304 is communicativelycoupled to the high-frequency transceiver circuit 306 via an electricalconnection 1340 and is communicatively coupled to the low-frequencytransceiver circuit 308 via an electrical connection 1342. Additionally,the processor 304 is communicatively coupled to the signal-limitingcircuits 1310, 1312, 1314, 1316 via electrical connections 1344, 1346,1348, 1350, respectively. It should be appreciated that the electricalconnections 1340, 1342, 1344, 1346, 1348, 1350 may be embodied as anytype of electrical connections that allow the processor 304 tocommunicate with the corresponding circuits and otherwise perform thefunctions described herein. For example, in some embodiments, theelectrical connections 1340, 1342 may be embodied as digital controlconnections that allow the processor 304 to interact with thehigh-frequency transceiver circuit 306 and the low-frequency transceivercircuit 308 via a SPI interface. Further, in some embodiments, theelectrical connections 1344, 1346, 1348, 1350 may be embodied as generalpurpose input/output (GPIO) connections that allow the processor 304 tointeract with the signal-limiting circuits 1310, 1312, 1314, 1316 (e.g.,electrical switches).

Similar to the communication circuit 300 of FIGS. 3-5, the illustrativeprocessor 304 is configured to control the signal-limiting circuits1310, 1312, 1314, 1316 of the communication circuit 1300 of FIG. 13 toselectively couple the high-frequency transceiver circuit 306 and thelow-frequency transceiver circuit 308 to the single element antenna 302for communication with remote devices via the corresponding carrierfrequency. For example, in a first mode of operation, the processor 304controls the signal-limiting circuits 1310, 1312, 1314, 1316 toelectrically couple/connect the high-frequency transceiver circuit 306to the single element antenna 302 and decouple/disconnect thelow-frequency transceiver circuit 308 from the single element antenna302. Accordingly, in the first mode of operation, the processor 304 isconfigured to power and received data from RF devices 104, 106 (e.g.,the smartcard 110) over the high frequency carrier frequency (e.g.,13.56 MHz). In the first mode of operation in which the high-frequencytransceiver circuit 306 is electrically coupled to the single elementantenna 302 for communication over the high frequency carrier frequency,it should be appreciated that the portions 1318, 1322 of the singleelement antenna 302 exhibit one or more electromagnetic characteristicsof resonant stubs (i.e., the portions 1318, 1322 act as one or morepassive RF components/elements), which are filtered by thehigh-frequency transceiver circuit 306. In a second mode of operation,the processor 304 controls the signal-limiting circuits 1310, 1312,1314, 1316 to electrically couple/connect the low-frequency transceivercircuit 308 to the single element antenna 302 and decouple/disconnectthe high-frequency transceiver circuit 306 from the single elementantenna 302. Accordingly, in the second mode of operation, the processor304 is configured to power and received data from RF devices 104, 106(e.g., the proximity card 108) over the low frequency carrier frequency(e.g., 125 kHz).

More specifically, in the first mode of operation in which communicationvia the high-frequency transceiver circuit 306 is enabled, thesignal-limiting circuit 1310 is in the state in which the first node1324 is decoupled from the terminal 1336, the signal-limiting circuit1312 is in the state in which the second node 1326 is electricallycoupled to the terminal 1332, the signal-limiting circuit 1314 is in thestate in which the third node 1328 is electrically coupled to theterminal 1334, and the signal-limiting circuit 1316 is in the state inwhich the fourth node 1330 is decoupled from the terminal 1338. In thesecond mode of operation in which communication via the low-frequencytransceiver circuit 308 is enabled, the signal-limiting circuit 1310 isin the state in which the first node 1324 is electrically coupled to theterminal 1336, the signal-limiting circuit 1312 is in the state in whichthe second node 1326 is decoupled from the terminal 1332, thesignal-limiting circuit 1314 is in the state in which the third node1328 is decoupled from the terminal 1334, and the signal-limitingcircuit 1316 is in the state in which the fourth node 1330 iselectrically coupled to the terminal 1338.

As described above, it should be appreciated that the single elementantenna 302 may be embodied as any type of antenna having a singleshared conductive element suitable for performing the functionsdescribed herein and otherwise consistent with the description. Forexample, in the illustrative embodiment, the single element antenna 302is embodied as a coil antenna and, in some embodiments, the singleelement antenna 302 may be structured such that its coils are physicallypositioned, partially or entirely, on the same shared plane as oneanother (e.g., printed on or integrated within a PCB substrate, a flexPCB, and/or another suitable substrate). In such embodiments, it shouldbe appreciated that the portion 1318 of the single element antenna 302is embodied as first portion of coils, the portion 1320 is embodied as asecond portion of coils, and the portion 1322 is embodied as a thirdportion of coils. As such, in the first mode of operation, the secondportion of coils is used for transmitting and receiving wirelesscommunication using the high-frequency transceiver circuit 306 and thefirst portion and third portion of coils have one or moreelectromagnetic characteristics of a resonant stub, which may beaccounted for by the high-frequency transceiver circuit 306. In thesecond mode of operation, the first portion, second portion, and thirdportion of coils are used for transmitting and receiving wirelesscommunication using the low-frequency transceiver circuit 308.

As indicated above, the single element antenna 302, the processor 304,the high-frequency (HF) transceiver circuit 306, and the low-frequency(LF) transceiver circuit 308 may be similar to the correspondingcircuits and components of the communication circuit 300 of FIG. 3. Assuch, it should be appreciated that, in some embodiments, the singleelement antenna 302 may be embodied as an antenna similar to the singleelement coil antennas 600, 700, 800 of FIGS. 6-8 but modified to accountfor the additional signal-limiting circuit in the communication circuit1300. Similarly, in some embodiments, the high-frequency transceivercircuit 306 of FIG. 13 may be embodied as a high-frequency transceivercircuit similar to the high-frequency transceiver circuit 900 of FIG. 9and/or the low-frequency transceiver circuit 308 of FIG. 13 may beembodied as a low-frequency transceiver circuit similar to thelow-frequency transceiver circuit 1000 of FIG. 10. Further, in someembodiments, one or more of the signal-limiting circuits 1310, 1312,1314, 1316 may be embodied as, or replaced by, filter circuits in thecommunication circuit 1300 in a manner similar to that described abovein reference to FIG. 11. In yet another embodiment, the signal-limitingcircuits 1310, 1312, 1314, 1316 may be omitted from the communicationcircuit 1300 in a manner similar to that described above in reference toFIG. 12.

According to one embodiment, a communication circuit may include asingle element antenna, a high-frequency transceiver circuit, alow-frequency transceiver circuit, a first switch, a second switch, anda third switch. The single antenna may include a first node, a secondnode, and a third node, wherein a first portion of the single elementantenna is defined between the first node and the second node and asecond portion of the single element antenna is defined between thesecond node and the third node. The high-frequency transceiver circuitmay have a first terminal and a second terminal, and wherein thehigh-frequency transceiver circuit enables wireless communication with afirst transponder over a high frequency carrier frequency. Thelow-frequency transceiver circuit may have a third terminal and a fourthterminal, and wherein the low-frequency transceiver circuit enableswireless communication with a second transponder over a low frequencycarrier frequency. The first switch electrically may be coupled to thefirst node and configured to be switched between a first state in whichthe first node is electrically coupled to the first terminal and asecond state in which the first node is electrically coupled to thethird terminal. The second switch may be electrically coupled to thesecond node and configured to be switched between an open state and ashort state in which the second node is electrically coupled to thesecond terminal. The third switch may be electrically coupled to thethird node and configured to be switched between an open state and ashort state in which the third node is electrically coupled to thefourth terminal.

In some embodiments, communication over the high-frequency transceivercircuit may be enabled when the first switch is in the first state andthe second switch is in the short state, and communication over thelow-frequency transceiver circuit may be enabled when the first switchis in the second state and the third switch is in the short state. Insome embodiments, the first portion of the single element antenna mayinclude a first conductive coil of a first diameter and the secondportion of the single element antenna may include a second conductivecoil of a second diameter different from the first diameter. In someembodiments, the first portion of the single element antenna may includea first conductive coil having a first number of windings and the secondportion of the single element antenna may include a second conductivecoil having a second number of windings different from the first number.In some embodiments, the high-frequency transceiver circuit may accountfor resonant stub properties of the second portion of the single elementantenna. In some embodiments, the low frequency carrier frequency isnominally 125 kHz. In some embodiments, the high frequency carrierfrequency is nominally 13.56 MHz.

In some embodiments, the communication circuit may further include acontrol circuit configured to control the first switch, the secondswitch, and the third switch. Further, the control circuit may switchthe first switch to the first state, the second switch to the shortstate, and the third switch to the open state for communication with thefirst transponder over the high frequency carrier frequency via thehigh-frequency transceiver circuit, and the control circuit may switchthe first switch to the second state, the second switch to the openstate, and the third switch to the short state for communication withthe second transponder over the low frequency carrier frequency via thelow-frequency transceiver circuit. In some embodiments, the controlcircuit includes a microcontroller. In some embodiments, thelow-frequency transceiver circuit may be disconnected from the singleelement antenna during communication over the high frequency carrierfrequency, and the high-frequency transceiver circuit may bedisconnected from the single element antenna during communication overthe low frequency carrier frequency. In some embodiments, each of thefirst switch, the second switch, and the third switch comprises one of arelay, a transistor, or a solid state relay.

According to another embodiment, a communication circuit may include asingle element antenna, a plurality of signal-limiting circuits, ahigh-frequency transceiver circuit, and a low-frequency transceivercircuit. The high-frequency transceiver circuit may be adapted to beselectively coupled to the single element antenna via the plurality ofsignal-limiting circuits and tuned to operate at a high frequencycarrier frequency, and the low-frequency transceiver circuit may beadapted to be selectively coupled to the single element antenna via theplurality of signal-limiting circuits and tuned to operate at a lowfrequency carrier frequency.

In some embodiments, the communication circuit may further include aprocessor and a memory comprising a plurality of instructions storedthereon that, in response to execution by the processor, causes thecommunication circuit to control the plurality of signal-limitingcircuits to couple the high-frequency transceiver circuit to the singleelement antenna and decouple the low-frequency transceiver circuit fromthe single element antenna for communication at the high frequencycarrier frequency during a first mode of operation, and control theplurality of signal-limiting circuits to couple the low-frequencytransceiver circuit to the single element antenna and decouple thehigh-frequency transceiver circuit from the single element antenna forcommunication at the low frequency carrier frequency during a secondmode of operation.

In some embodiments, the single element antenna may include a resonantstub when the high-frequency transceiver circuit is coupled to thesingle element antenna and the low-frequency transceiver circuit isdecoupled from the single element antenna, and the high-frequencytransceiver circuit may filter one or more electromagneticcharacteristics of the resonant stub. In some embodiments, thecommunication circuit may be configured to power and receive data from asmartcard during the first mode of operation. In some embodiments, thecommunication circuit may be configured to power and receive data from aproximity card during the second mode of operation. In some embodiments,the low frequency carrier frequency is nominally 125 kHz. In someembodiments, the high frequency carrier frequency is nominally 13.56MHz.

In some embodiments, the single element antenna may include a firstnode, a second node, a third node, and a fourth node, wherein a firstportion of the single element antenna is defined between the first nodeand the second node, a second portion of the single element antenna isdefined between the second node and the third node, and a third portionof the single element antenna is defined between the third node and thefourth node; the high-frequency transceiver circuit may have a firstterminal and a second terminal; the low-frequency transceiver circuitmay have a third terminal and a fourth terminal; and the plurality ofsignal-limiting circuits may include a first signal-limiting circuitelectrically coupled to the first node and configured to transitionbetween a state in which the first node is decoupled form the thirdterminal and a state in which the first node is electrically coupled tothe third terminal, a second signal-limiting circuit electricallycoupled to the second node and configured to transition between a statein which the second node is decoupled from the first terminal and astate in which the second node is electrically coupled to the firstterminal, a third signal-limiting circuit electrically coupled to thethird node and configured to transition between a state in which thethird node is decoupled from the second terminal and a state in whichthe third node is electrically coupled to the second terminal, and afourth signal-limiting circuit electrically coupled to the fourth nodeand configured to transition between a state in which the fourth node isdecoupled from the fourth terminal and a state in which the fourth nodeis electrically coupled to the fourth terminal.

According to yet another embodiment, a communication circuit formulti-frequency communication may include a single element antenna, ahigh-frequency transceiver circuit, and a low-frequency transceivercircuit. The single element antenna may include a plurality of coils,wherein the plurality of coils consists of a first portion of coils anda second portion of coils. The high-frequency transceiver circuit may beadapted to be selectively coupled to the single element antenna in afirst mode of operation of the communication circuit in which wirelesscommunication with a first RF communication device at a high frequencycarrier frequency via the single element antenna is enabled. Thelow-frequency transceiver circuit may be adapted to be selectivelycoupled to the single element antenna in a second mode of operation ofthe communication circuit in which wireless communication with a secondRF communication device at a low frequency carrier frequency via thesingle element antenna is enabled. In the first mode of operation, thefirst portion of coils may be used for transmitting and receiving thewireless communication with the first RF communication device and thesecond portion of coils may have one or more electromagneticcharacteristics of a resonant stub. In the second mode of operation, thefirst portion of coils and the second portion of coils may be used fortransmitting and receiving the wireless communication with the second RFcommunication device. In some embodiments, the high-frequencytransceiver circuit may enable wireless communication with a smartcardat a nominal carrier frequency of 13.56 MHz, and the low-frequencytransceiver circuit may enable wireless communication with a proximitycard at a nominal carrier frequency of 125 kHz.

What is claimed is:
 1. A communication circuit, comprising: a singleelement antenna including a first node, a second node, and a third node,wherein a first portion of the single element antenna is defined betweenthe first node and the second node and a second portion of the singleelement antenna is defined between the second node and the third node; ahigh-frequency transceiver circuit having a first terminal and a secondterminal, and wherein the high-frequency transceiver circuit enableswireless communication with a first transponder over a high frequencycarrier frequency; a low-frequency transceiver circuit having a thirdterminal and a fourth terminal, and wherein the low-frequencytransceiver circuit enables wireless communication with a secondtransponder over a low frequency carrier frequency; a first switchelectrically coupled to the first node and configured to be switchedbetween a first state in which the first node is electrically coupled tothe first terminal and a second state in which the first node iselectrically coupled to the third terminal; a second switch electricallycoupled to the second node and configured to be switched between an openstate and a short state in which the second node is electrically coupledto the second terminal; and a third switch electrically coupled to thethird node and configured to be switched between an open state and ashort state in which the third node is electrically coupled to thefourth terminal.
 2. The communication circuit of claim 1, whereincommunication over the high-frequency transceiver circuit is enabledwhen the first switch is in the first state and the second switch is inthe short state; and wherein communication over the low-frequencytransceiver circuit is enabled when the first switch is in the secondstate and the third switch is in the short state.
 3. The communicationcircuit of claim 1, wherein the first portion of the single elementantenna comprises a first conductive coil of a first diameter and thesecond portion of the single element antenna comprises a secondconductive coil of a second diameter different from the first diameter.4. The communication circuit of claim 1, wherein the first portion ofthe single element antenna comprises a first conductive coil having afirst number of windings and the second portion of the single elementantenna comprises a second conductive coil having a second number ofwindings different from the first number.
 5. The communication circuitof claim 1, wherein the high-frequency transceiver circuit accounts forresonant stub properties of the second portion of the single elementantenna.
 6. The communication circuit of claim 1, wherein the lowfrequency carrier frequency is nominally 125 kHz.
 7. The communicationcircuit of claim 1, wherein the high frequency carrier frequency isnominally 13.56 MHz.
 8. The communication circuit of claim 1, furthercomprising a control circuit configured to control the first switch, thesecond switch, and the third switch; wherein the control circuitswitches the first switch to the first state, the second switch to theshort state, and the third switch to the open state for communicationwith the first transponder over the high frequency carrier frequency viathe high-frequency transceiver circuit; and wherein the control circuitswitches the first switch to the second state, the second switch to theopen state, and the third switch to the short state for communicationwith the second transponder over the low frequency carrier frequency viathe low-frequency transceiver circuit.
 9. The communication circuit ofclaim 8, wherein the control circuit comprises a microcontroller. 10.The communication circuit of claim 8, wherein the low-frequencytransceiver circuit is disconnected from the single element antennaduring communication over the high frequency carrier frequency; andwherein the high-frequency transceiver circuit is disconnected from thesingle element antenna during communication over the low frequencycarrier frequency.
 11. The communication circuit of claim 1, whereineach of the first switch, the second switch, and the third switchcomprises one of a relay, a transistor, or a solid state relay.
 12. Acommunication circuit, comprising: a single element antenna; a pluralityof signal-limiting circuits; a high-frequency transceiver circuitadapted to be selectively coupled to the single element antenna via theplurality of signal-limiting circuits and tuned to operate at a highfrequency carrier frequency; and a low-frequency transceiver circuitadapted to be selectively coupled to the single element antenna via theplurality of signal-limiting circuits and tuned to operate at a lowfrequency carrier frequency.
 13. The communication circuit of claim 12,further comprising: a processor; and a memory comprising a plurality ofinstructions stored thereon that, in response to execution by theprocessor, causes the communication circuit to (i) control the pluralityof signal-limiting circuits to couple the high-frequency transceivercircuit to the single element antenna and decouple the low-frequencytransceiver circuit from the single element antenna for communication atthe high frequency carrier frequency during a first mode of operation,and (ii) control the plurality of signal-limiting circuits to couple thelow-frequency transceiver circuit to the single element antenna anddecouple the high-frequency transceiver circuit from the single elementantenna for communication at the low frequency carrier frequency duringa second mode of operation.
 14. The communication circuit of claim 12,wherein the single element antenna comprises a resonant stub when thehigh-frequency transceiver circuit is coupled to the single elementantenna and the low-frequency transceiver circuit is decoupled from thesingle element antenna; and wherein the resonant stub is a component ofthe high-frequency transceiver circuit.
 15. The communication circuit ofclaim 12, wherein the communication circuit is configured to power andreceive data from a smartcard during the first mode of operation. 16.The communication circuit of claim 12, wherein communication circuit isconfigured to power and receive data from a proximity card during thesecond mode of operation.
 17. The communication circuit of claim 12, thelow frequency carrier frequency is nominally 125 kHz.
 18. Thecommunication circuit of claim 12, wherein the high frequency carrierfrequency is nominally 13.56 MHz.
 19. The communication circuit of claim12, wherein the single element antenna includes a first node, a secondnode, a third node, and a fourth node, wherein a first portion of thesingle element antenna is defined between the first node and the secondnode, a second portion of the single element antenna is defined betweenthe second node and the third node, and a third portion of the singleelement antenna is defined between the third node and the fourth node;wherein the high-frequency transceiver circuit has a first terminal anda second terminal; wherein the low-frequency transceiver circuit has athird terminal and a fourth terminal; wherein the plurality ofsignal-limiting circuits includes a first signal-limiting circuitelectrically coupled to the first node and configured to transitionbetween a state in which the first node is decoupled form the thirdterminal and a state in which the first node is electrically coupled tothe third terminal, a second signal-limiting circuit electricallycoupled to the second node and configured to transition between a statein which the second node is decoupled from the first terminal and astate in which the second node is electrically coupled to the firstterminal, a third signal-limiting circuit electrically coupled to thethird node and configured to transition between a state in which thethird node is decoupled from the second terminal and a state in whichthe third node is electrically coupled to the second terminal, and afourth signal-limiting circuit electrically coupled to the fourth nodeand configured to transition between a state in which the fourth node isdecoupled from the fourth terminal and a state in which the fourth nodeis electrically coupled to the fourth terminal.
 20. A communicationcircuit for multi-frequency communication, the communication circuitcomprising: a single element antenna including a plurality of coils,wherein the plurality of coils consists of a first portion of coils anda second portion of coils; a high-frequency transceiver circuit adaptedto be selectively coupled to the single element antenna in a first modeof operation of the communication circuit in which wirelesscommunication with a first RF communication device at a high frequencycarrier frequency via the single element antenna is enabled; and alow-frequency transceiver circuit adapted to be selectively coupled tothe single element antenna in a second mode of operation of thecommunication circuit in which wireless communication with a second RFcommunication device at a low frequency carrier frequency via the singleelement antenna is enabled; wherein, in the first mode of operation, thefirst portion of coils is used for transmitting and receiving thewireless communication with the first RF communication device and thesecond portion of coils has one or more electromagnetic characteristicsof a resonant stub; and wherein, in the second mode of operation, thefirst portion of coils and the second portion of coils are used fortransmitting and receiving the wireless communication with the second RFcommunication device.
 21. The communication circuit of claim 20, whereinthe high-frequency transceiver circuit enables wireless communicationwith a smartcard at a nominal carrier frequency of 13.56 MHz; andwherein the low-frequency transceiver circuit enables wirelesscommunication with a proximity card at a nominal carrier frequency of125 kHz.